CD19 is a transmembrane protein found on the cell surface that is involved in establishing intrinsic B cell signaling thresholds through modulating both B cell receptor (BCR)-dependent and independent signaling.1
CD19 is thought to play dual roles in B cell activation:
- As an adaptor protein to recruit cytoplasmic signaling proteins to the membrane
- As a signal subunit for the CD19/CD21 complex when bound with the BCR, where antigen-bearing complement enhances B-cell activation via BCR-CD19/CD21 binding
CD19 also has other roles such aiding in the regulation of bone marrow development and plays a role in B cell development from early differentiation events in the bone marrow to late maturation steps in the spleen. CD19 signaling may play a role in controlling the progression of early pre-B to small, resting pre-B cells in the bone marrow by associating with components of the pre-BCR.